The invention relates generally to AC electrical machines and, more particularly, to a dual magnetic phase material rings for use in such electrical machines.
The need for high power density and high efficiency electrical machines (i.e., electric motors and generators) has long been prevalent for a variety of applications, particularly for hybrid and/or electric vehicle traction applications. The current trend in hybrid/electric vehicle traction motor applications is to increase rotational speeds to increase the machine's power density, and hence reduce its mass and cost. However, it is recognized that when electrical machines are used for traction applications in hybrid/electric vehicles, there is a clear tradeoff between power density, efficiency, and the machine's constant power speed range—and that this tradeoff presents numerous design challenges.
Specifically, magnetic materials used in rotating electric machines generally serve multiple functions. Efficient coupling of magnetic fluxes to complementary poles across an air gap in the electric machines are desirable. Soft magnetic materials of the magnetic components may also bear a significant fraction of the mechanical and structural loads of the electric machine. Sometimes there may be tradeoffs between efficient magnetic utilization of the material and mechanical load bearing capability of the magnetic materials. Alternatively, sometimes speed rating of a machine may be lowered in order to allow a machine topology with efficient magnetic utilization. Therefore, it is desirable to have a material that can avoid the trade-offs between efficiency and operability of the electric machines by locally controlling the magnitude of the saturation magnetization of the soft magnetic material used in electric machines.
The power density of an electric machine may be increased by increasing the machine size, improving thermal management, increasing rotor speed, or by increasing the magnetic utilization. The magnetic utilization may be increased by using a combination of processing and alloying of a rotor lamination to create a multi-phase magnetic material by developing localized areas of high and low permeability. The localized areas of high and low permeability generally reduce flux losses during rotor operation.
However, while the use of multi-phase magnetic material rotor laminations increases the magnetic utilization of the electric machine, thereby minimizing the flux leakage path and increasing the high-speed power and torque capability of the induction machine without sacrificing power density or efficiency, there are drawbacks associated with such multi-phase magnetic material rotor laminations. That is, the use multi-phase magnetic material rotor laminations results in a lack of saturation flux density as compared to conventional rotor laminations. This low saturation flux density leads to lower power densities in dual phase laminated electric machines, especially under low speed conditions and high saturation conditions.
Therefore, it would be desirable to provide an electric machine, and associated motor components, that provide for reduced leakage reactance in order to improve a high speed performance of the machine, while also providing for the recovery of low speed power densities. It would further be desirable for such components of the electric machine to be provided as add-on components useable with conventional laminations, such that manufacturing of rotors and stators of the electric machine are simplified and the design of the electric machine is not changed substantially.